Whenever people design aquatic humanoids (be they mermaids or other ''mer-folk'' type creatures) that do not breath water with lungs but through gills i often see those gills placed either on the neck (throat) or on the chest (often roughly spaced out between the ribs).
What would seems the most biologically logical (as far as the entire concept can be considered logical anyway) place for gills to evolve on a humanoid creature, the neck/throat, on the chest or between the back (joints) of the lower jaw and the neck?